1. Field of the Invention
The present invention relates to a touch sensor capable of determining whether a valid touch has been given by a finger, or the like.
2. Description of the Related Art
Touch sensors are roughly divided into electric sensors using a change in impedance, such as capacitance, resistance, etc., optical-coupling sensors, mechanical sensors, and the like.
Among electric sensors, capacitive sensors using capacitance, in particular, allows detecting a touch even with a small touch pressure. At the same time, the capacitive sensors are highly sensitive, and thus react on a touch by an object or an unintended human body to perform detection.
In order not to detect a touch when an object is placed on a touch sensor, or in order to prevent an unintended touch by a human body, there is a method of providing an operation face 101 of a touch sensor at a position lower than a surface 100 as shown in FIG. 5A.
For example, a description has been given of a capacitive control member, which is a touch sensor of a capacitive type, an optical-coupling type, etc., in Japanese Unexamined Patent Application Publication No. 2004-006315. The description includes a support structure made of a hard material, which is difficult to be elastically deformed, is provided with a through hole having a size corresponding to a human finger. The through hole is covered with an elastic cover, and a touch-sensor operation section (in the case of a capacitor, an electrode, etc., thereof) is disposed at a predetermined position just under the through hole.
This sensor structure is devised with the intention of knowing the position of the operation section (touch section) of the touch sensor without seeing in the following circumstances. For example, the sensor is used for a touch sensor, etc., on the operation panel of an in-vehicle unit using the difference between touch feeling when tracing by a finger on the elastic cover of the hard support structure and touch feeling when tracing by a finger on the portion of only the elastic cover at the edge and the inside of the through hole.
However, in the case of the sensor structure described in Japanese Unexamined Patent Application Publication No. 2004-006315, even if an object is placed on the sensor, the sensor does not detect it. Also, if the sensor is unintentionally touched by a part other than a human finger, for example, a palm of a human hand or by an arm, the sensor does not detect it.
Thus, the sensor structure described in Japanese Unexamined Patent Application Publication No. 2004-006315 has an advantage for preventing an unintentional touch by an object and a person and for detecting only a valid touch.
In particular, in order to prevent an unintended touch by an object, it is possible to substantially achieve the prevention by inclining a sensor operation face 102 to such a degree not allowing to place an object as shown in FIG. 5B.